Dissertation / PhD Thesis

FZJ-2014-01754

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Pulvermetallurgische Funktionsbauteile aus NiTi- und NiTi-X Legierungspulvern

Bitzer, M. (Corresponding author)FZJ*

2014
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/5959

Abstract: Powder metallurgy is an attractive option for manufacturing of NiTi parts considering its limited machinability due to the shape memory effect. Nevertheless, the industrial implementation of this process for NiTi-alloys is not trivial due to need of demonstrating reproducible shape memory behaviour which is strongly influenced by the high affinity for oxygen and carbon. O- and C-rich phases as well as the precipitation of Ni-rich Ni$_{4}$Ti$_{3}$ occuring by the cooling process from process temperature influence the transformation behaviour. In the present work, each step of the powder metallurgical production-chain is discussed, starting from prealloyed NiTi-powder and ending with functional components. Three innovative applications with high industrial relevance were used for demonstrating the high potential of P/Mtechnologies: Orthodontic NiTi-brackets with pseudoelastic properties at body temperature were manufactured by Metal-Injection-Moulding (MIM). Required phase transformation temperatures were adjusted by heat treatment. Fully pronounced shape memory effect was demonstrated using the one way effect. Futhermore it was shown, that blending prealloyed NiTi-powder with elemental Ni or Ti is a promising approach for shifting transformation temperatures as well as reducing the residual porosity after sintering by the formation of an eutectic melt. NiTi is an attractive material for cavitation resistant coatings considering its clearly pronounced damping behaviour based on its pseudoelastic properties. Cavitation might cause significant wear in technical applications like turbine blades in hydropower plants or pump components. Coating of exposed surfaces by wear resistant materials would be highly attractive for extending lifetime of related systems. A promising powder metallurgical processing route for manufacturing such coatings is Low Pressure Plasma Spraying (LPPS). In the present work, NiTi-layers were produced by LPPS, starting from prealloyed NiTi-powder. Cavitation resistance depending on LPPS parameters, surface treatment and layer thickness was investigated. The study is accompanied by characterization of microstructure and phase transformation behaviour. Compared to binary NiTi, ternary NiTi-X-alloys differ in phase transformation behavior and can thereby enlarge the application field of shape-memory-alloys. In the case of addition of elemental Nb, broadening of hysteresis between austenitic and martensitic phase transformation temperatures after plastic deformation of the Nb-phase is a well-known effect, which is the key of function of coupling elements already established on the market. In the present study, Nb, W and Ag were blended with prealloyed NiTi-powder and hot isostatic pressing was used for manufacturing NiTi-Nb, NiTi-Ag and NiTi-W-alloys for the production of couplings. Microstructures, interdiffusion phenomena, phase transformation behavior, and impurity contents were investigated aiming on better understanding of the influence of insoluble phases on bulk properties of NiTi-SMAs. Due to its antibacterial properties, NiTi-Ag is furthermore a promising alloy for medical implants. Biocompatibility and toxicity with respect to bacteria were investigated for evaluating the potential of the material for this application.

Keyword(s): Dissertation

Note: Universität Bochum, Diss., 2013

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Contributing Institute(s):

1. Werkstoffsynthese und Herstellungsverfahren (IEK-1)

Research Program(s):

1. 123 - Fuel Cells (POF2-123) (POF2-123)

Appears in the scientific report 2014

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Database coverage:

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